There are numerous patents and prior art proposals relating to processes for the anionic polymerization of 2-pyrrolidone using a wide variety of catalysts, activators or initiators. Among the earliest patents are U.S. Pat. Nos. 2,638,463; 2,739,959; 2,809,958; 2,891,038 and 2,973,343.
Various activators are mentioned in U.S. Pat. Nos. 2,912,415; 3,016,366; 3,022,274; 3,028,369; 3,033,831; 3,040,004; 3,042,659; 3,060,153; 3,061,593; 3,135,719; 3,148,174; 3,158,589; 3,174,951; 3,180,855 and 3,210,324.
The most recent which claim CO.sub.2 as the sole polymerization activator are U.S. Pat. Nos. 3,681,293; 3,682,869 and 3,683,046 relating to the polymerization of 2-pyrrolidone but either various grades of polymer or industrially unfeasible processes were obtained.
According to these and subsequent patents, the polymerization of 2-pyrrolidone was considered to be an anionic polymerization caused by the rupture of the 2-pyrrolidone ring between the C.dbd.O and N--H groups to form a linear polyamide polymer which has come to be known as Nylon-4;
HAVING THE STRUCTURE: ##STR1## This polymer is melt-spinnable to form fibers having the strength and wear resistance of synthetic fibers and the advantageous chemical properties of cotton, such as water-absorptivity and release, dye-receptivity and similar ironing capability.
Subsequently there have been proposals of hydrogen transfer processes for the polymerization of 2-pyrrolidone also based upon the rupture of the 2-pyrrolidone ring between the C.dbd.O and N--H group, as in U.S. Pat. Nos. 3,069,392 and 3,383,367.
It is not certain whether such known hydrogen transfer processes are based upon an inaccurate theory, but it is clear that such processes also provide a polymer which is relatively low in yield, are economically not feasible and/or provide a polymer which is modified by the reaction with the activators therewith to become a part of the polymer chain and cause other complications in further processing of the finished polymer.
It is clear that while there are numerous patents relating to a variety of processes proposed over the years for the polymerization of 2-pyrrolidone, such a polymer has never been produced commercially to the best of my knowledge at the present time.